DXOMark has released their review of the Canon EOS R image sensor. I've never really put much stock in the testing at DXOMark, but there are a lot of people that do. The EOS R, which has a nearly identical image sensor, but different DIGIC version (DIGIC 8 vs DIGIC 6+) to the EOS 5D Mark IV actually scored 2 points lower at 89. The EOS 5D Mark IV scored a 91.
Although we’ve not directly compared the two Canon 30MP full-frame CMOS sensors side-by-side in this review, it’s not surprising that the results for the EOS R are very close to that of the Canon EOS 5D Mark IV. Both appear to use a similar sensor, with some of the differences likely attributable to the increased number of AF points available in the EOS R.
While not possessing the low noise levels of the Nikon Z 6 and Sony A7 III, which have slightly lower pixel density and BSI architecture in their favor, the EOS R’s sensor is one of Canon’s best. It comes very close to the one used in the pro-level EOS 1Dx Mark II, particularly in its low light, high ISO capabilities.
With a low noise floor, the dynamic range of the Canon 30MP sensor greatly improves over its predecessors. The EOS R is much more capable of handling high-contrast scenes, thus allowing a photographer faced with protecting highlights at capture to lift shadows in post-processing without incurring some of the noise penalties. Read the full review
The review is mostly positive for the image sensor in the EOS R, and after using the EOS R for some time, I've found no issues with the quality of the image sensor. I'm one of those crazy people that doesn't care about dynamic range though, which can bring about some fun conversations at parties.